Author(s)

K. Tokaji & S. Takahishi

Abstract

Fatigue fracture process with fish-eye in gas nitrided low alloy steel K.Tokaji' & S.Takahashi * Department of Mechanical and Systems Engineering, Gifii University, Gifu, Japan, 2 Engineering Department, Toeikanki Co., Ltd., Gifu, Japan. Abstract This paper describes the fatigue fracture process with a fish-eye in gas-nitrided low alloy steel (Cr-Mo steel). Cantilever type rotary bending fatigue tests have been conducted in laboratory air at ambient temperature using specimens with different nitride case depths. It was found that the fatigue strength increased with increasing case depth. Subsurface crack initiation was observed in all nitrided materials regardless of case depth and stress level. A fish-eye was always seen with an inclusion at its center from which cracks originated. Based on some detailed fractographic analyses of fish-eyes, it was indicated that the fatigue fracture process of the nitrided materials was dominated by the crack growth from inclusion to the

Keywords